I am very suspicious that your girl may have pyometra.
This is a life-threatening infection of the uterus, where the uterus fills with bacteria and white blood cells. It often occurs at this time of year, as unspayed cats will start to go into heat in January or February. If they don’t get pregnant, then the uterus is a high risk for infection developing.
If the cervix is open, the pus will drip out, and will look creamy-white to yellow as you have described. It often has a foul FOUL odour.
If the cervix happens to be closed, there is no visible discharge from the vagina and all the pus stays inside the cat. This is much more dangerous. The toxins in the pus are absorbed in to the blood stream and the cat becomes very ill.
Without treatment, pyometra can be fatal.
The best treatment is to spay your cat and thus remove the source of infection, though some cats may respond to antibiotic treatment if the cervix is open.
Here is more about pyometra in cats:
And here is a site that you can use in the USA to find free or or low cost spaying and neutering:
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The above is given for information only. Although I am a licensed veterinarian, I cannot legally prescribe medicines or diagnose your pet's condition without performing a physical exam. If you have concerns about your pet I would strongly advise contacting your regular veterinarian.